1. Field of the Invention
The present invention relates to a device for reducing rf-induced audio noise generated within a hearing aid of a user of an associated portable wireless device (PWD). Additionally, the present invention relates to a device for reducing the specific absorption rate (SAR) of the associated PWD during operation.
2. Description of the Related Art
In-ear hearing aid use may be limited during operation of certain types of PWDs due to rf-induced audio noise generated within the hearing aid while in operation near a transmitting PWD. The noise is induced during PWD transmission as an electromagnetic field from the PWD induces currents in the circuitry of the hearing aid. The electromagnetic field from the PWD causes components within the hearing aid to generate audio noise, the noise being particularly related to the frequencies of the digital portion of the PWD. Solutions to this problem having included: moving the PWD away from the ear/head by providing a 2-way audio link between the remote PWD and the ear. Two types of such audio links are a) a xe2x80x9cdocking stationxe2x80x9d for the PWD that has microphone/speaker, and b) a xe2x80x9cT-coilxe2x80x9d that couples audio from the cellphone into the hearing aid. Another solution to the problem has been a wired connection of a microphone/speaker unit from the PWD to the vicinity of the user""s head. The microphone/speaker unit requires insertion of a small xe2x80x9cspeakerxe2x80x9d into the user""s ear, which may not be possible for the user of an in-ear hearing aid. Further, the wire(s) may allow RF to flow from the PWD""s antenna system into the microphone/speaker unit and subsequently cause similar audio noise as if the PWD were near the head.
A solution to this hearing aid noise / PWD problem that permits the hearing impaired to use a conventional PWD, particularly a digital cellphone, in the normal manner without an accessory speaker/microphone device would be desirable.
Current digital cellphones are designed for operation on multiple frequency bands, for instance the 824-894 and 1850-1990 MHz bands in the US. Band selection is done without user input, and is determined by band availability in a particular geographical area. Both US frequency bands provide digital service, therefore a solution to the hearing aid noise problem caused by digital cellphones must be compatible with each frequency bands used by the cellphone.
SAR (specific absorption rate) for users of PWDs is a matter of increasing concern. RF radiation to the user""s head results from the free-space generally omnidirectional radiation pattern of typical current PWD antennae. When PWDs equipped with such an antenna are placed near the user""s head, the antenna radiation pattern is no longer omnidirectional as radiation in a large segment of the azimuth around the user is blocked by the absorption/reflection of the head. An antenna system for PWDs that greatly reduces radiation to the body and redirects it in a useful direction is also desirable.
FIG. 1 illustrates a prior art dual-band PIFA antenna 30, which is located on the rear of a personal wireless device (xe2x80x9cPWDxe2x80x9d) 32, and electrically connected to ground plane 34 at one end and capacitively coupled to ground plane 34 at another end. PWD 32 further includes a battery pack 35 positioned away from antenna 30. In normal operation, PWD 32 is oriented in an upright manner so that end 38 is generally above end 40. Ground plane 34 is provided by the ground traces of the printed wiring board (PWB) of PWD 32. The portion of antenna 30 indicated by numeral 42 resonates over a higher frequency band, while the entire portion 42, 44 of antenna 30 resonates over a lower frequency band. PIFA antenna 30 is grounded at its upper end at location indicated as numeral 46 to ground plane 34. PIFA antenna 30 is capacitively coupled at pad 48 in a direction away from upper end 38 of PWD. This type of antenna provides some reduction in SAR, but cannot eliminate hearing aid noise from a digital PWD.
Referring to FIG. 2, a perspective view of a prior art PWD 32 (in the form of a cellphone) used in the vicinity of a hearing aid 60 is illustrated. Cellphone 32 has a speaker on the keyboard surface near the top of the phone, which is normally aligned with the center of the user""s ear 62 during use. Hearing aid 60 may be any type, including in-ear and behind-ear variations. Hearing aid 60 has an amplified audio output port 4, which is inserted into the ear canal of the ear 62. During operation, an electromagnetic field 64 is generated around cellphone 32 by omnidirectional antenna 66. In operation, electromagnetic field 64 illuminates the hearing aid 60, user""s ear 62, and the user""s head. RF noise is induced in the hearing aid by the field 64, resulting in excessive audio noise being presented to the user.
The device of the present invention greatly reduces radiation directed toward a user""s head and hearing aid during device operation. As a result, the device promotes a reduction or elimination of hearing aid noise and SAR. Other benefits include longer transmit/receive range, lower transmit power, and longer battery life.
A device according to the present invention may include a PWD implemented for operation over single or multiple frequency-bands. An antenna may be incorporated within a PWD at the time of manufacture, or may be provided as an accessory or after market item to be added to existing PWD""s having an external antenna port. The latter feature is particularly useful, in that existing PWD""s can be retrofitted to achieve the benefits of the antenna of the present invention, including elimination of hearing aid noise and very low SAR. The antenna of the present invention is suitable for high-volume, low cost manufacturing. The antenna/PWD combination, whether an aftermarket or original equipment item, may be placed in a leather or plastic case, such that the antenna side of the PWD is facing away from the body. This provides a further advantage with respect to SAR, when the PWD is stored via a belt clip when in receive-only mode.
Other objects of the present invention include:
the elimination (or substantial reduction) of audio noise in hearing aids caused by close proximity to transmitting PWDs, particularly digital cellphones;
the elimination (or substantial reduction) of audio noise in hearing aids caused by close proximity to transmitting PWDs, particularly PWD""s operating in one or more frequency bands, enabling use of hearing aids in close proximity to such PWDs;
the reduction in SAR due to operation of a single or multi-band PWD near the user""s head;
the provision of an antenna suitable for integration within or upon a PWD;
the provision of an antenna having wide bandwidth in one or more frequency bands;
the provision of an antenna having one or more active elements and one or more passive elements, each resonant on one or more frequency bands;
the provision of an antenna which radiates RF energy from a PWD preferentially away from a user thereof;
the provision of an antenna promoting increased PWD battery life by reducing commanded RF power;
the provision of an antenna having a reduction in the amount of RF energy beingabsorbed by a user""s hand during operation; and
the provision of an antenna with the one or more active element(s) connected to a PWD""s transmit/receive port.
These and further objects of the present invention will become apparent to those skilled in the art with reference to the accompanying drawings and detailed description of preferred embodiments, wherein like numerals refer to like parts throughout.